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Radiation Protection Flashcards

1
Q

Background radiation dose to a member of public??

A

2.5mSv

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2
Q

What is Air Kerma?

A

Total Kinetic energy released per unit mass by an ionising radiation

Units Gy

Measurement in air used as air has a similar atomic number to soft tissue (7) and effect on radiation on changes in temp are so small that they can be ignored.

At lower dose: AIR KERMA = ABSORBED DOSE

At higher doses: AIR KERMA > ABSORBED DOSE

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3
Q

Absorbed dose?

A

Amount of deposited energy in a substance

Units of Gy

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4
Q

Relationship between:

Absorbed dose

Equivilent dose

Effective dose

A

Absorbed dose in Gy

multiply by Radiation weighting factor

Equivilent dose in Sv

multiply by tissue weighting factor (had no units)

Effective dose in Sv
(absorbed dose weighted for ratiosensitvity of tissue)

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5
Q

What is Radiation weighting factor?

A

Takes into account effects of different types of radiation

Alpha particles highest: 20

Protons: 2

X-ray, beta, gamma, positrons: 1

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6
Q

Does effective dose relate to stochastic or deterministic effect?

A

Risk of stochastic effects in linked to the EFFECTIVE DOSE

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7
Q

What are the tissue weighting factors?

A

A value given to the different organ sensitivies to radiation

Bone, colon, lung, breast: 0.12

Gonads: 0.08

Skin and brain: 0.01

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8
Q

When is the highest risk to the fetus?

A

All or nothing effect during early fetal stage (0 - 2 weeks)

First trimester is very sensitive: high incidence of congenital malformations

Childhood cancer biggest risk in FIRST TRIMESTER

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9
Q

What is threshold dose for CNS malformations to fetus?

A

100 - 200mGy

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10
Q

When to suspend breastfeeding?

A

Completly if: had course of I131

3 weeks if:

  • I131, I125
  • Gallium
  • Sodium
  • Thallium

12 hours after:

  • Iodine 131 hippurate
  • All Technetium 99m compounts (except Tc red cells which is 4 hours)

4 hours:

  • Technetium 99m red cells
  • DTPA
  • Phosphonates
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11
Q

Effective Dose limits for employee >18years

(Effective Dose governs STOCHASTIC effect risk)

A

20mSv per year

or

100mSv in any consecutive 5 years (with a max of 50mSv per any single year)

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12
Q

Effective dose limits for trainee <18 years

A

6mSv

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13
Q

Effective dose limit for <16 year (trainee or anyone)

A

1mSv per year

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14
Q

Dose to abdomen for person of reproductive capacity (STAFF)

A

13mSv in any consecutive 3 months

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15
Q

What is DAP?

A

DAP = entrance skin dose x cross sectional area of x-ray beam

  • A measure of patient exposure
  • Not affected by distance

Units Gy/cm2

The DAP meter must intercept the ENTIRE area of the x-ray beam

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16
Q

Equivilent dose limits?

Deterministic

A

Lens: 20mSv over 18 years

15mSv under 18 years and indirectly from another person

Extremeties and Skin: 500mSv over 18 years

150mSv for under 18 years

50mSv for thosse exposed indirectly after exposure of another person

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17
Q

What is controlled area?

4 points

A

Where person working their may be subject to:

  1. Effective dose >6mSv
  2. Lens dose 15mSv
  3. Equivilent dose of 3/10 of any relevant dose limit
  4. External dose rates 7.5microSv/hour averaged over the day
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18
Q

What is supervised area?

A

If anyone in the area is likely to receive a dose of 1mSv/year or 1/10th or any dose limit

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19
Q

When to notify HSE?

A
  • Doses exceed staff dose limits
  • Exposures much greater than intended
  • Loss or theft or source
  • Release of spillage leading to significant contamination
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20
Q

What is yearly background radiation dose?

A

2.7mSv approx

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21
Q

Radiation dose - flights etc

A
  • Transatlantic flight: 0.08mSv
  • Nucleur power station worker: 0.18mSv
  • Annual average radon dose: 1.3mSv (out of total 2.7mSv average) - over 50% of dose
  • Average annual radon dose in Cornwall: 6.9mSv

Radon gas emits alpha particles

Medical contribution = 14% to yearly dose

  • CT contributes 47% of medical dose and is only 4% of exams

Nucleur Fallout (from testing of Nucleur weapons years ago)

  • dose is so minimum, just 0.2%
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22
Q

What causes direct damage to tissues?

A

Rupture of Covalent bonds

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23
Q

What causes indirect damage to tissues?

A

Production of free radicals

Free radicals cause chemical changes in tissues

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24
Q

Are absorbed doses higher or lower than effective dose?

A

Absorbed doses tend to be higher

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25
What is the average radiation dose per hour of flying?
**4µSv/hour**
26
What do tissue weighting factors give an indication of?
An estimate of the **MORTALITY** from cancers per mSv to that organ or tissue Do not account for likelihood of getting cancer
27
Does Skin and Bone surface have same tissue weighting factor?
Yes 0.01
28
Deterministic dose effects
Lowest is fetal abnormality is **0.1 - 0.5Gy** Most things is **2 - 5Gy** **_Cataracts is 5Gy_** Fatal whole body dose is **5Gy** _Deterministic effect gets more severe as dose increases_
29
What is equivilent dose limit for the abdomen of a female employee of reproductive age?
13mSv in **3 months**
30
Who has overall responsibility for radiation protection?
Employer
31
What is justification?
Justification to carry out or decline an examination if: * benefit of doing exam outweighs risk (carry out exam) * benefit of doing exam does not outweigh risk (decline to do exam)
32
Governing body of IRR?
HSE (Health and safety excecutive)
33
Gornerning body of IRMER for reporting overexposures to patients?
CQE (Care quality commission)
34
Barium doses
Barium meal - 3mSv Barium enema - 7mSv
35
Does absorbed dose depend on organ mass?
NO
36
Time of greatest risk of foetal abnormalities?
First trimerster 3 - 8 weeks
37
Mental retardation?
First and second trimester 8 - 15th week
38
Childhood cancer risk?
Maximal in **first trimester**
39
Risk of fatal cancer from exposure?
1 in 20,000 per **mSv** Or 5% per **sievert**
40
Risk of childhood cancer from exposure in utero?
1 in 33,000 per **mGy** 3% per **gray**
41
What does radon produce?
Alpha particles
42
What can DAP ionisation chamber be used for?
* x-ray * fluoro **NOT CT**
43
TLDs
Have: * linear response over wide dose range * generally used with filters * can be reused. can only be read out once * can detect shallow and deep doses * **Have similar sensitivity to film dose badges** * can measure finger and eye doses * **Precision of 15% for low doses** * **Precision of 3% for high doses** **_Need heated to 300 degrees for read out_** **_Need to be annealed after read out_** **_TLD holder helps differentiate between skin and deeper doses_** Disadvantages: * cannot measure dose rate * cannot differentiate between radiation types * affected by heat
44
Film Badges
Advantages: * can identify type of exposure * Highly energy depdendent due to the different atomic numbers of Silver and Bromide * **sensitivity is 0.1mSv** * use double sided film emulsion (without a screen) * similar sensitivity to TLDs * provide a permanent record * can detect beta radiation and radioactive splash **No intensifier on a film badge** Disadvantages: * prone to fogging * must be developed and read out * require calibration
45
OSL Badges Optically stimulated luminescence
Use aluminium oxide Intensity of luminescence is proportional to the absorbed dose _Can read dose as low as **0.01mSv**_
46
Electronic dosimeters
* Accurate to 1µSv * Require a filter * 100 times more sensitive than TLDs * Provide a direct reading * can be used to detect radioactive contamination **ARE HIGHLY ENERGY DEPENDENT** * Geiger muller counters are counted as electronic dosimeters too
47
Can secondary electrons cause ionization?
Yes
48
Are writing protocols for doses and having medical physics expert part of IRMER or IRR?
Part of IRMER
49
Radiation protection supervisor duties?
* Investigation of excessive doses * ensuring staff follow local rules * ensuring QA processes in place * risk assessment for pregnant staff
50
Can DAP be converted into effective dose?
Yes * Can be converted into **EFFECTIVE DOSE** using conversion factor * Conversion factors depend on the region of the body
51
DRLs Are they set locally?
* Are set for standard sized patients (not taken into account for overweight folk) * **Yes they are set locally by employer but they must be close to the nationally set DRLs** DRLs are set using ESD, screening times and DAP as references
52
Wall protection requirements?
**Lead - 2mm** **Concrete - 1.5cm** **Barium plaster - 2cm** **Brick - 2.4cm** (equals 2mm of lead)
53
Pregnant worker
Should inform **EMPLOYER** Should not need to alter her working practice
54
Pointers
* Leakage of radiation should be less than 1mGy per hour at distance of 1m * Operator should stand **2m** from x ray tube * Filtration in dentistry is 1.5mm aluminium * Lead apron 45 x 40cm long
55
Does risk of stochastic effects increase LINEARLY or exponentially with dose?
Increases **Linearly** **Known as the Linear no threshold theory** Increased risk with lower age (kids more likely to get a cancer than an adult) For stochastic effects: * Risk of leukaemia is usually peaking at around 7 years * Risk of solid organ tumour is around 40 years
56
Who are overexposures due to equipment fault reported to?
Has to reported under IRR if it is due to equipment Reported to HSE
57
IRR
* Employer must state their intention to HSE about using ionising equipment for FIRST time (not for equipement change) * Employers responsibilty to perform a risk assessment before installing new equipment (not manufacturers responsibility)
58
Yearly effective dose limit for: Adults/Under 18/Carer comforter
**Adult \>18: 20mSv** **Under 18: 6mSv** **Member of public or under 16: 1mSv** **Carer of comforter: 5mSv in any period over 5 years**
59
Who governs testing of equipment?
IRMER and IRR
60
What is a dose constraint?
It is the maximum dose than can be **exceeded**
61
Dose to adults per year. Can it exceed 20mSv/year?
Yes it can as long as it doesnt exceed: **50mSv in a single year** **100mSv over 5 years**
62
What can DRLs be expressed as?
* **Screening time** * **mA** * **kV** * **DAP**
63
How much radiation does lead apron transmit? 0.35mm
**0.35mm transmits 3%** **0.25mm transmits 5%**
64
What are the remainder organs in tissue weighting factors?
* Kidneys * Adrenal * Gallbladder * Heart * Lymph nodes * Muscles * Pancreas * Uterus * Prostate * Small bowel * Thymus **All 0.01 each**
65
Changes new in IRR17
66
Lead Aprons
67
Radiation Doses for different exams
68
Radiation protection advisor and medical physics expert IRMER or IRR
Medical physics expert - IRMER RPA - IRR
69
RPS and RPA
70
Is equivilent dose used to set occupational dose organ limits?
Yes

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